1. Field of the Invention
This invention relates to an improved apparatus for capacitive pressure sensing devices.
2. Prior Art
There are many capacitive pressure sensing devices in the prior art. These devices are manufactured from various materials and in various ways. The capabilities of such devices generally are limited by the known methods and devices.
For example, construction of the sensing diaphragm from an electrically non-conductive material such as quartz has known advantages as described, for example, in German Offenlegungschrift No. 2021479. U.S. Pat. No. 3,962,921 shows a pressure sensitive capacitive construction using two diaphragms 36 and 38, however, these diaphragms are "secured by bonding" but no method of bonding is taught. U.S. Pat. No. 4,084,438 teaches a method of bonding diaphragms or discs by having the discs "peripherally bounded by a predetermined curve" establishing a "predetermined gap" with "a plurality of shims . . .". The '438 specification states: "Then the discs are pressed together and fused by applying heat and pressure at localized regions near those spaced points. Then the shims are removed and the remaining points on the peripheral boundary are similarly fused by the application of heat and pressure at localized regions of the disc elements near the remaining peripheral points." Such construction causes internal stresses, which are acknowledged in the patent by the statements that "internal stress developed during the fusion process . . ." may be reduced by annealling. The present invention in a unique manner avoids this problem and provides several advantages which will be apparent to a skilled artisan from the disclosure.